Air-conditioning system for vehicle

ABSTRACT

An air-conditioning system for a vehicle according to the present invention has an ECU which executes a control routine for controlling the cooling performance of a refrigeration circuit during vehicle acceleration. The control routine includes the steps of detecting demanded vehicle-acceleration degree, detecting evaporator exit air temperature at the time vehicle acceleration starts, selecting acceleration-period cooling performance on the basis of the demanded acceleration degree and the exit air temperature, and outputting a capacity control signal to a compressor on the basis of the acceleration-period cooling performance selected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an air-conditioning system for a vehicle,specifically, an air-conditioning system comprising a variable capacitycompressor.

2. Description of the Related Art

A variable capacity compressor provided in an air-conditioning systemfor a vehicle can regulate the cooling performance of theair-conditioning system, or in other words, the cooling performance ofthe refrigeration circuit thereof by its refrigerant discharge capacitybeing varied. Specifically, under the conditions such that the thermalload in a passenger compartment of the vehicle is high, as in summer,the compressor is driven to operate with a maximum refrigerant dischargecapacity. This causes a drop in the temperature of conditioned air blownout into the compartment so that the compartment temperature isregulated to a level comfortable to the vehicle occupant.

When the compressor is driven to operate with the maximum refrigerantdischarge capacity during acceleration of the vehicle, however, thedrive power consumed by the compressor greatly increases with anincrease in rotation speed of an engine equipped with the vehicle, whichcauses a great decrease in the acceleration performance of the vehicle.In this connection, there has been already developed a technique ofdecreasing the drive power supplied to the compressor when anacceleration of the vehicle is detected (see the Patent document:Japanese Unexamined Patent Publication No. Sho 57-175422, for example).In this technique, the part of engine output corresponding to thedecrease in drive power supplied to the compressor is allocated forvehicle traveling, so that the acceleration performance of the vehicleis ensured.

When the drive power supplied to the compressor is unconditionallydecreased during vehicle acceleration, the conditioned-air temperaturehowever rises so that the compartment temperature cannot be maintainedat a level comfortable to the vehicle occupant.

Thus, there is observed a trade-off between maintaining the comfortablecompartment temperature and ensuring the vehicle accelerationperformance.

Such trade-off problem may be solved by decreasing the drive powersupplied to the compressor in a manner such that the conditioned-airtemperature is kept within a desirable range so that the comfortablecompartment temperature is maintained, during the vehicle acceleration.In order to achieve this, consideration needs to be given to the degreeof acceleration demanded by the driver and the conditioned-airtemperature, when the vehicle is accelerated.

The Patent Document, however, gives no consideration to this point.Thus, according to the Patent Document, for example even in a situationthat the conditioned-air temperature is close to the upper limit of aset range for allowing the compartment temperature to be maintained whenvehicle acceleration is started, the drive power supplied to thecompressor is consistently decreased according to a demand for thevehicle acceleration. Consequently, the conditioned-air temperaturerises, so that the compartment temperature rises above the set range,i.e., the comfortable compartment temperature cannot be maintained.

The primary object of the present invention is to provide anair-conditioning system for a vehicle that can ensure the vehicleacceleration performance and at the same time maintain the comfortablecompartment temperature.

SUMMARY OF THE INVENTION

The above object is achieved by an air-conditioning system for a vehicleaccording to the present invention, the system comprises:

a refrigeration circuit including a circulation path along which arefrigerant circulates, the refrigeration circuit having a variablecapacity compressor, a condenser, an expansion mechanism and anevaporator disposed in the circulation path in this order;

a degree detection device for detecting demanded vehicle-accelerationdegree;

a temperature detection device for detecting temperature of theevaporator or temperature correlating with the temperature of theevaporator, at vehicle-acceleration start time;

a selection device for selecting acceleration-period cooling performanceof the refrigeration circuit, on the basis of the demanded accelerationdegree and the temperature detected; and

an output device for generating a capacity control signal fordetermining an amount of the refrigerant discharged from the compressor,on the basis of the acceleration-period cooling performance selected,and outputting the capacity control signal to the compressor.

According to the air-conditioning system described above, in selectingthe cooling performance of the refrigeration circuit to decrease thedrive power supplied to the compressor during vehicle acceleration, thedemanded acceleration degree and the temperature are taken intoconsideration. Thus, during the vehicle acceleration, the coolingperformance selected does not arbitrarily decreased. This makes itpossible to ensure the vehicle acceleration performance and at the sametime maintain the comfortable compartment temperature of the vehicle.

The demanded acceleration degree can be obtained from the amount ofaccelerator depression given by the driver, for example. The temperatureis the temperature of exit air, namely air after passing through theevaporator.

Preferably, the selection device should have control modes forcontrolling the acceleration-period cooling performance of therefrigeration circuit, where selection from the control modes isperformed on the basis of a difference between pre-acceleration coolingperformance of the refrigeration circuit at the acceleration start timeand post-acceleration cooling performance of the refrigeration circuitestimated in consideration of vehicle acceleration. Specifically, thecontrol modes can include a HOLD mode to be selected when the differenceis within a specified range, that is, the difference is so small that itdoes not have a significant influence on the vehicle accelerationperformance or the comfortable compartment temperature, for maintainingthe acceleration-period cooling performance at the same level as thepre-acceleration cooling performance.

When the HOLD mode is selected, the acceleration-period coolingperformance is maintained at the same level as the pre-accelerationcooling performance, so that the comfortable compartment temperature ismaintained during the vehicle acceleration. Thus, the air-conditioningsystem has an improved reliability.

The control modes can include at least one of an UP mode and an DOWNmode to be selected when the difference is out of a specified range,that is, the difference is so great that it has a significant influenceon the comfortable compartment temperature or the vehicle accelerationperformance. The UP mode maintains the acceleration-period coolingperformance at a higher level compared with the pre-acceleration coolingperformance, and the DOWN mode contrarily maintains theacceleration-period cooling performance at a lower level compared withthe pre-acceleration cooling performance.

When the UP mode is selected, the acceleration-period coolingperformance is maintained at a higher level compared with thepre-acceleration cooling performance, so that the comfortablecompartment temperature is maintained even during the vehicleacceleration. Meanwhile, when the DOWN mode is selected, theacceleration-period cooling performance is maintained at a lower levelcompared with the pre-acceleration cooling performance, so that afurther increase in vehicle acceleration performance is achieved.

Preferably, the UP mode should be provided to cause theacceleration-period cooling performance to increase with an increase inthe temperature detected, while the DOWN mode should be provided tocause the acceleration-period cooling performance to decrease with anincrease in the demanded acceleration degree.

The selection device may be adapted to calculate an acceleration-periodtarget temperature for the evaporator, on the basis of the demandedacceleration degree and the temperature detected, and set theacceleration-period cooling performance on the basis of thisacceleration-period target temperature, where the acceleration-periodtarget temperature should desirably be a target temperature for exitair, namely air after passing through the evaporator.

Alternatively, the selection device may be adapted to calculate anacceleration-period target pressure for the compressor, on the basis ofthe demanded acceleration degree and the temperature of exit air, andset the acceleration-period cooling performance on the basis of thisacceleration-period target pressure, where the acceleration-periodtarget pressure should desirably be a target intake pressure at whichthe compressor should suck in the refrigerant.

Whether the acceleration-period cooling performance is calculated on thebasis of the target temperature for the evaporator or the targetpressure for the compressor as mentioned above, the acceleration-periodcooling performance calculated is such that makes it possible to ensurethe vehicle acceleration performance and at the same time maintain thecomfortable compartment temperature.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the sprits and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus, are notlimitative of the present invention, and wherein:

FIG. 1 schematically shows an embodiment of an air-conditioning systemfor a vehicle;

FIG. 2 is a control block diagram for an A/C ECU of FIG. 1;

FIG. 3 is a flow chart showing a control procedure executed by controlblocks of FIG. 2;

FIG. 4 is a graph showing relation between threshold for determiningvehicle acceleration and vehicle speed;

FIG. 5 is a diagram for explaining how to determine whether the vehicleis being accelerated or not, on the basis of accelerator depression;

FIG. 6 is a diagram for explaining how to select a control mode;

FIG. 7 is a graph showing relation between exit air temperature from anevaporator at the vehicle-acceleration start time and parameter α;

FIG. 8 is a graph showing relation between demanded vehicle-accelerationdegree and parameter β;

FIG. 9 is a graph showing how HOLD, UP and DOWN modes for controllingacceleration-period cooling performance are distributed with respect todemanded acceleration degree and exit air temperature;

FIG. 10 is a graph showing a controllable region and an uncontrollableregion for the compressor, defined depending on capacity control signal;

FIG. 11 is a graph for explaining how the system operates when the HOLDmode is selected;

FIG. 12 is a graph for explaining how the system operates when the UPmode or DOWN mode is selected;

FIGS. 13 to 16 are diagrams showing variants of control blocks of FIG.2;

FIG. 17 is a graph showing relation between demanded acceleration degreeand target intake pressure for the compressor;

FIG. 18 is a graph showing relation between exit air temperature andtarget intake pressure for the compressor;

FIG. 19 is a graph showing relation between demanded acceleration degreeand target exit air temperature in acceleration-period of the vehicle;and

FIG. 20 is a graph showing relation between exit air temperature andtarget exit air temperature.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically shows a part including an engine room 2. A vehicleis provided with an air-conditioning system, and this system comprises arefrigeration circuit 4. The refrigeration circuit 4 has a refrigerantcirculation path, and by a refrigerant circulating along the circulationpath, the temperature of the vehicle interior is regulated to within arange set as desired.

Specifically, in the circulation path, a variable capacity compressor 6,a condenser 8, a liquid receiver, also called simply a receiver 10, anexpansion valve (expansion mechanism) 12 and an evaporator 14 aredisposed in this order. The compressor 6, condenser 8, receiver 10 andexpansion valve 12 are arranged in the engine room 2, while theevaporator 14 is located within a ventilation duct 16. The ventilationduct 16 is arranged behind the engine room 2.

In the present embodiment, the compressor 6 is driven by an engine (notshown) of the vehicle. Specifically, the compressor 6 includes anelectromagnetic clutch 7, and the electromagnetic clutch 7 is disposedin a power transmission path for connecting the engine and thecompressor 6. When a start switch (not shown) for the air-conditioningsystem is put in an ON position, the electromagnetic clutch 7 allowstransmission of power from the engine to the compressor 6 so that thecompressor 6 is driven.

Within the ventilation duct 16, a blower 18 is disposed upstream of theevaporator 14. The blower 18 is driven by a motor 19. Further, a heaterunit 22 is disposed downstream of the evaporator 14. The heater unit 22includes a water valve 23 and an air mixing damper 21. The air mixingdamper 21 regulates the ratio between the flow quantity of air passingthrough the heater unit 22 and the flow quantity of air bypassing theheater unit 22.

When driven, the compressor 6 sucks in the refrigerant in the state of adry vapor, from the evaporator 14 side, and compresses the suckedrefrigerant and discharges it in the state of a high-temperature andhigh-pressure gas, toward the condenser 8. The refrigerant discharged iscooled and condensed into a liquid state within the condenser 8, and theliquid refrigerant is supplied from the condenser 8 to the receiver 10,at the same pressure, and stored in the receiver 10 temporarily.

Then, the high-pressure liquid refrigerant is delivered from thereceiver 10 towards the expansion valve 12. When passing through theexpansion valve 12, the liquid refrigerant expands, so that therefrigerant in the state of a wet vapor, namely a liquid and vapormixture at low temperature and low pressure spurts out into theevaporator 14 and is evaporated within the evaporator 14.

At this time, the evaporation heat cools the air passing through theevaporator 14 by the heat exchange in the evaporator 14. The air passingthrough the evaporator 14 is inside air inside the passenger compartmentof the vehicle and/or outside air outside the compartment, which isintroduced through an inlet 24 into the ventilation duct 16 and flowedtoward the evaporator 14 by means of the blower 18.

The air cooled is blown out into the compartment, as conditioned air,through at least one of DEF-side, VENT-side and FOOT-side outlets 26, 27and 28, and cools the compartment.

The refrigerant evaporated into a gas state within the evaporator 14returns to the compressor 6, and is again compressed by the compressor 6and circulates as described above.

In the present embodiment, in addition to an ECU (electronic controlunit) 50 for the engine, an ECU 60 for air-conditioning is provided inthe compartment. The ECUs 50, 60 each comprise an input-output device,memory (ROM, RAM, BURAM, etc.) for storing control programs, controlmaps, etc., a central processing unit (CPU), a timer counter, etc.,although not shown in the drawings.

To the input of the ECU 50, sensors, such as a rotation speed sensor 38for detecting engine rotation speed Ne, a water temperature sensor 40for detecting engine coolant temperature Tw, an accelerator depressionsensor 42 for detecting accelerator depression quantity Da, i.e., theamount of depression of an accelerator pedal (not shown) given by thedriver, and a vehicle speed sensor 44 for detecting vehicle speed V, areelectrically connected. Sensor signals from these sensors 38 to 44 aretransmitted from the ECU 50 to the ECU 60, through a CAN (ControllerArea Network).

To the input of the ECU 60, sensors, such as a temperature sensor 30 fordetecting temperature of the evaporator 14, specifically, thetemperature of the exit air at the evaporator 14, which will be referredto as exit air temperature Te_a, a temperature sensor 32 for detectingoutside air temperature Tamb, a temperature sensor 34 for detecting thetemperature of air in the compartment, which will be referred to ascompartment temperature Tr, and a solar radiation sensor 36 fordetecting solar radiation quantity Sun, are electrically connected. Tothe output of the ECU 60, the electromagnetic clutch 7 of the compressor6 and an amplifier 20 for the motor 19 are electrically connected.

The ECU 60 has a function of varying the amount of the refrigerantdischarged from the compressor 6, during vehicle acceleration.Specifically, the ECU 60 supplies a capacity control signal I to thecompressor 6. The capacity control signal I controls the amount of therefrigerant discharged from the compressor 6 so that the intake pressureat which the compressor 6 sucks in the refrigerant will become equal toa target value. As a result of this control, the cooling performance ofthe refrigeration circuit 4 is determined.

Next, the function of the ECU 60 will be described in detail.

As shown in FIG. 2, the ECU 60 includes a determination section 62 fordetermining target temperature for exit air, i.e., air after passingthrough the evaporator 14. To the determination section 62, presettemperature Tr_for air conditioning of the compartment, compartmenttemperature Tr, outside air temperature Tamb and solar radiationquantity Sun are supplied, and the determination section 62 determinestarget air temperature Te_o on the basis of these quantities supplied.The target air temperature Te_o determined is supplied from thedetermination section 62 to an output section 76 for the capacitycontrol signal I.

The preset temperature Tr_s is stored in the memory of the ECU 60. Inaddition to the preset temperature Tr_s, the memory also stores a presetvalue “BLV” for the blower 18, a preset value “Intake” which determinesa ratio between inside air and outside air for the air passing throughthe evaporator 14, a preset value “Mode” for setting a mode forselecting an outlet through which conditioned air should be blown out,etc. These preset values are set by operating setting switches on adashboard in the compartment.

The ECU 60 includes a gate section 64. To the gate section 64, exit airtemperature Te_a is supplied from the temperature sensor 30. The gatesection 64 is caused to open temporarily at the time the vehicleacceleration starts, and sends out an exit air temperature Te_a as anexit air temperature Te_b at the acceleration start time. The exit airtemperature Te_b is supplied from the gate section 64 to an estimationsection 72 for target intake pressure of the refrigerant and a selectionsection 74 for cooling performance. The opening and closing of the gatesection 64 will be described later.

The estimation section 72 estimates target intake pressure Ps_o of therefrigerant, which is the intake pressure of the compressor 6 at theacceleration start time, from the exit air temperature Te_b, andsupplies it to the output section 76. It is to be noted that theestimation section 72 may estimate the target intake pressure Ps_o,taking account of parameters such as the outside air temperature Tamb,the rotation speed of the compressor 6, the engine rotation speed Ne,the engine coolant temperature Tw, etc., in addition to the exit airtemperature Te_b. In that case, the accuracy of estimation of the targetintake pressure Ps_o is extremely high. Further, in place of estimatingthe target intake pressure Ps_o, if an intake pressure sensor fordetecting the intake pressure at which the refrigerant is taken into thecompressor 6 is provided to the compressor 6, the intake pressuredetected by the intake pressure sensor at the time the vehicleacceleration starts can be used as the target intake pressure Ps_o.

The ECU 60 further includes a threshold setting section 66, and vehiclespeed V is supplied to the setting section 66. On the basis of thevehicle speed V, the setting section 66 sets a threshold TH foraccelerator depression quantity Da, for use in determining whether ornot vehicle acceleration has started. The threshold TH and theaccelerator depression quantity Da are supplied to a calculation section68 for demanded acceleration degree.

On the basis of the accelerator depression quantity Da and the thresholdTH, the calculation section 68 calculates demanded acceleration degreeAr_d of the vehicle by the driver, and supplies it to the selectionsection 74. It is to be noted that the demanded acceleration degree Ar_dmay be calculated by using, in place of the accelerator depressionquantity Da, a physical quantity correlating with the acceleratordepression quantity Da, such as the opening of the throttle valvedisposed in the intake passage of the engine.

The selection section 74 first calculates post-acceleration coolingperformance Qpost of the refrigeration circuit 4, which is estimated inconsideration of vehicle acceleration, on the basis of the demandedacceleration degree Ar_d and the exit air temperature Te_b at theacceleration start time of the vehicle, and then calculates a differenceΔQ between this post-acceleration cooling performance Qpost andpre-acceleration cooling performance Qpre, i.e., the cooling performanceat the acceleration start time, according to the equation:

ΔQ=Qpost−Qpre

Then, taking account of the influence which the difference ΔQ has on theacceleration performance of the vehicle and the compartment temperatureTr comfortable to the vehicle occupant(s), the selection section 74selects a cooling performance control mode X and transmits the selectedcontrol mode X to the output section 76.

When the vehicle is in a traveling state other than acceleration, theoutput section 76 calculates a capacity control signal In_a on the basisof the target air temperature Te_o supplied from the determinationsection 62, and supplies a capacity control signal I set to the capacitycontrol signal In_a, to the compressor 6.

Meanwhile, when the vehicle is under acceleration, the output section 76calculates a capacity control signal Ia that determinesacceleration-period cooling performance of the refrigeration circuit, onthe basis of a basic capacity control signal Io calculated on the basisof the target intake pressure Ps_o and the control mode X selected bythe selection section 74, and supplies a capacity control signal I setto the capacity control signal Ia, to the compressor 6.

FIG. 3 shows a control flow chart executed by the ECU 60.

First, at step S301, detection signals from the above-mentioned sensorsand preset values stored in the memory are read. Then at step S302, thetarget air temperature Te_o (determination section 62) and the capacitycontrol signal In_a (output section 76) are calculated by the equationsbelow:

Te _(—) o=f(Tr _(—) s,Tr,Tamb,Sun)

In _(—) a=f(Te _(—) o)

Then, at step S303, the threshold TH for use in determining whether ornot the vehicle acceleration is starting is set (setting section 66).Specifically, suppose that the vehicle is traveling at a fixed vehiclespeed V, the higher vehicle speed V, the greater accelerator depressionDa the driver gives. Thus, the threshold TH needs to be set to a greatervalue for a higher vehicle speed V, as shown in FIG. 4. Thus, at stepS303, the threshold TH corresponding to the vehicle speed V is set fromthe map of FIG. 4.

Next at step S304, the demanded acceleration degree Ar d is calculated(calculation section 68) according to the equation:

Ar _(—) d=Da−TH

Then at step S305, whether or not the vehicle is under acceleration isdetermined. Specifically, as shown in FIG. 5, just now the acceleratordepression quantity Da reaches the threshold TH or just after theaccelerator depression quantity Da exceeds the threshold TH, thedetermination at step S305 changes to Yes, that is, the accelerationdetermination changes from “OFF” to “ON”. At this time, the calculationsection 68 supplies an open signal Sd to the gate section 64 (see FIG.2), thereby causing the gate section 64 to open temporarily as mentionedabove.

It is to be noted that when the accelerator depression quantity Dadecreases from the threshold TH or above, the acceleration determinationchanges from “ON” to “OFF” at the time the accelerator depressionquantity Da becomes a specified amount H smaller than the threshold TH.The acceleration determination map thus includes a hysteresis loop toprevent hunting in acceleration determination.

When the determination at step S305 is No, next step S306 is executed,where the capacity control signal I is set to the capacity controlsignal In_a and supplied to the compressor 6 (output section 76). Thenat step S307, “0” is set in a flag, and then step S301 and thesucceeding steps are repeated.

When the determination at step S305 is Yes, i.e., it is determined thatthe vehicle is under acceleration, step S308 is executed, where whetheror not the flag is “0” is determined.

When this is the first time that the determination at step S308 iscarried out after executing of step S307, or in other words, when it isimmediately after the vehicle has transferred from a non-accelerationstate to an acceleration state, the determination at step S308 is Yes,so that step S309 is executed next. If the determination at step S308 isNo, step S301 and the succeeding steps are repeated.

At step S309, the ECU 60 selects a control mode X (selection section74).

Specifically, first, the post-acceleration cooling performance Qpost andthe pre-acceleration cooling performance Qpre are calculated accordingto the equations below:

Qpost=f(Te _(—) b,Ar _(—) d)

Qpre=f(Te _(—) b)

Then, a difference between the post-acceleration cooling performanceQpost and the pre-acceleration cooling performance Qpre, i.e.,ΔQ(=Qpost−Qpre) is calculated, and then, on the basis of the differenceΔQ, the cooling performance that the refrigerant circuit should attainduring the vehicle acceleration, that is, a control mode X forcontrolling the cooling performance during the acceleration period, isselected.

Specifically, as shown in FIG. 6, when the absolute value of thedifference ΔQ is less than or equal to a specified value ΔQth, HOLD modeis selected as a control mode X. The situation in which the HOLD mode isselected is that the difference ΔQ does not have a significant influenceon the acceleration performance of the vehicle or the compartmenttemperature Tr comfortable to the vehicle occupant(s).

When the difference ΔQ is positive and its absolute value is greaterthan the specified value ΔQth, UP mode is selected as a control mode X,and when the difference ΔQ is negative and its absolute value is greaterthan the specified value ΔQth, DOWN mode is selected as a control modeX. The situation in which the UP mode or DOWN mode is selected is thatthe difference ΔQ has a significant influence on the accelerationperformance of the vehicle or the compartment temperature Tr comfortableto the vehicle occupant(s).

Further, when the UP mode or DOWN mode is selected, mode strengthparameter α or β is set. Specifically, when the UP mode is selected,parameter α (>0) is set on the basis of the exit air temperature Te_b,where the parameter α is set to a greater value for a higher exit airtemperature Te_b, as shown in FIG. 7. Meanwhile, when the DOWN mode isselected, parameter β (>0) is set on the basis of the demandedacceleration degree Ar_d, where the parameter β is set to a greatervalue for a higher demanded acceleration level Ar_d, as shown in FIG. 8.

FIG. 9 shows an example of how the HOLD, UP and DOWN modes aredistributed, with respect to the demanded acceleration degree Ar_d andthe exit air temperature Te_b.

In FIG. 9, specified temperatures Te_o max and Te_o min are maximum andminimum values for the above-mentioned preset temperature Tr_s, i.e.,the temperature preset for air conditioning of the compartment. It is tobe noted that when the demanded acceleration degree Ar_d exceeds amaximum allowable value Ar_d_max, the air-conditioning system isstopped, and therefore the driving of the compressor 6 is stopped.

The situation in which the demanded acceleration degree Ar_d exceeds themaximum allowable value Ar_d_max is an emergency in which an extremelygreat vehicle acceleration is demanded by the driver. In such emergency,the engine output is allocated concentratedly for vehicle acceleration,to further increase the acceleration performance of the vehicle. It isto be noted that in the present embodiment, the compressor 6 is stoppedby disengaging the electromagnetic clutch 7. However, when thecompressor 6 is not provided with the electromagnetic clutch 7, thecapacity control signal I indicative of discharge quantity 0 is suppliedto the compressor 6.

After a control mode X is selected as described above, step S310 isexecuted, where the capacity control signal Ia that determines theacceleration-period cooling performance of the refrigeration circuit iscalculated (output section 76).

Specifically, first, a basic capacity control signal Io is calculatedaccording to the equation involving the target intake pressure Ps_o as aparameter:

Io=f(Ps _(—) o)

When the control mode X selected by the selection section 74 is the HOLDmode, the capacity control value Ia is obtained by the followingequation:

Ia=Io

Meanwhile, when the control mode X selected is the UP mode or the DOWNmode, the capacity control signal Ia is obtained by one of the followingequations:

Ia=Io+α

Ia=Io−β

Then, at step S311, whether or not the capacity control signal Ia isgreater than or equal to a minimum value needed for the refrigerationcircuit during acceleration is determined. When the result of thedetermination is Yes, i.e., it is determined that the capacity controlsignal Ia is within a controllable region as shown in FIG. 10, step S313is executed, where the capacity control signal I is set to the capacitycontrol signal Ia, as shown by the following equation:

I=Ia

Meanwhile, when the result of the determination at step S311 is No,i.e., it is determined that the capacity control signal Ia is smallerthan the minimum value Imin, step S312 is executed, where the capacitycontrol signal Ia is replaced by the minimum value Imin, as shown by theequation below, and then step S313 is executed.

Ia=Imin

After the capacity control signal I is determined in the above describedmanner, the capacity control signal I is supplied from the outputsection 76 to the compressor 6. Thus, the compressor 6 discharges therefrigerant of the amount corresponding to the capacity control signal Ito the circulation path of the refrigeration circuit 4. Consequently,the intake pressure Ps at which the compressor 6 sucks in therefrigerant is controlled to the desired value. Then, at step S314, “1”is set into the flag, and then step S301 and the succeeding steps arerepeated.

Once step S314 is executed, the result of the determination at step S308is No when step S308 is executed in the next cycle. Thus, as long as thevehicle stays under acceleration, step S309 and the succeeding steps arenot executed again. Thus, during vehicle acceleration, the capacitycontrol signal Ia is not replaced by a new capacity control signal. Evenif the amount Da of accelerator depression given by the driver slightlyvaries, such slight variation does not affect the capacity controlsignal Ia.

As clear from the above explanation, in the air-conditioning systemaccording to the present invention, the drive power supplied to thecompressor 6 is decreased during vehicle acceleration, but in that case,the decreasing rate of the drive power supplied to the compressor 6 isdetermined taking account of the degree of vehicle acceleration demandedor the accelerator depression quantity Da.

Specifically, in the above-described embodiment of the air-conditioningsystem, the selection section 74 selects a control mode X forcontrolling the acceleration-period cooling performance, on the basis ofthe demanded acceleration degree Ar_d and the exit air temperature Te_b.As control modes X, three modes, namely the HOLD, UP and DOWN modes areprovided, so that the cooling performance is prevented from being alwaysdecreased during the vehicle acceleration, compared with theacceleration start time. Thus, it is possible to ensure the accelerationperformance of the vehicle and at the same time maintain the compartmenttemperature Tr comfortable to the vehicle occupant(s).

More specifically, when the absolute value of the difference ΔQ is lessthan or equal to the specified value ΔQth, i.e., when the difference ΔQdoes not have a significant influence on the acceleration performance ofthe vehicle or the compartment temperature Tr comfortable to the vehicleoccupant(s), the selection section 74 selects the HOLD mode as a controlmode X. In this case, during vehicle acceleration, the drive power C_Psupplied to the compressor 6 varies as shown in solid line in FIG. 11.It is to be noted that C_T in FIG. 11 denotes the torque exerted on thecompressor 6.

In the HOLD mode, the capacity control signal Ia or the basic capacitycontrol signal Io is calculated on the basis of the target intakepressure Ps_o before acceleration of the vehicle. Thus, even when theengine rotation speed Ne increases, the drive power C_P supplied to thecompressor 6 does not greatly increase, in other words, an increase indrive power C_P is kept at a low level. Thus, the vehicle accelerationperformance does not suffer a significant decrease and therefore isensured. This means that the air-conditioning system has an improvedreliability.

Further, during vehicle acceleration, the situation where the drivepower C_P supplied to the compressor 6 is not decreased as shown indotted line in FIG. 11, to allocate the power corresponding to thedecrease in drive power C_P for vehicle acceleration does not occurs.Thus, during vehicle acceleration, the exit air temperature Te_b and theintake pressure Ps hardly vary as shown in solid line in FIG. 11. Thisensures that the comfortable compartment temperature Tr is maintainedduring vehicle acceleration.

To the contrary, if the drive power C_P supplied to the compressor 6 isdecreased during vehicle acceleration, the exit air temperature Te_b andthe intake pressure Ps greatly increase as shown in dotted line in FIG.11, so that the comfortable compartment temperature Tr cannot bemaintained. This always happens as long as the drive power C_P suppliedto the compressor 6 is decreased.

Meanwhile, when the selection section 74 selects the UP mode or the DOWNmode as a control mode X, the capacity control signal Ia is determinedby adding the parameter α to the basic capacity control signal Io orsubtracting the parameter β from the basic capacity control signal Io,as mentioned above. This means that the acceleration-period coolingperformance determined by the capacity control signal Ia is calculatedby taking account of the exit air temperature Te_b or the demandedacceleration degree Ar_d in addition to the pre-acceleration coolingperformance Qpre.

Specifically, when the UP mode is selected as a control mode X, thecapacity control signal Ia is set to the basic capacity control signalIo plus parameter α, so that, the exit air temperature Te_b and theintake pressure Ps are decreased during vehicle acceleration, comparedwith the acceleration start time, as shown in one-dot chain line in FIG.12. Consequently, the temperature of the conditioned air blown out intothe compartment is more decreased.

When the DOWN mode is selected as a control mode X, the capacity controlsignal Ia is set to the basic capacity control signal Io minus parameterβ, so that the torque C_T exerted on the compressor 6 is greatlydecreased during vehicle acceleration as shown in two-dot chain line inFIG. 12. Consequently, the vehicle acceleration performance increases.

It is to be noted that the curves shown in solid line in FIG. 12 relateto the case where the HOLD mode is selected as a control mode X.

The present invention is not limited to the above-described embodiment,but may be modified in various ways.

For example, as shown in FIG. 13, in place of the estimation section 72and the selection section 74, one calculation section 78 can be used.The calculation section 78 calculates acceleration-period target airtemperature Te_b_a, on the basis of the exit air temperature Te_b andthe demanded acceleration degree Ar_d, and supplies it to the outputsection 80. In this case, the output section directly calculates thecapacity control signal Ia from the acceleration-period target airtemperature Te_b_a, by the following equation:

Ia=f(Te _(—) b _(—) a)

Further, as seen from FIG. 14, a calculation section 82 can be used inplace of the selection section 74. The calculation section 82 calculatesacceleration-period target intake pressure Ps_o_a, on the basis of thetarget intake pressure Ps_o estimated by the estimation section 72 andthe demanded acceleration degree Ar_d, and supplies it to an outputsection 84. In this case, the output section 84 directly calculates thecapacity control signal Ia from the acceleration-period target intakepressure Ps_o_a by the following equation:

Ia=f(Ps _(—) o _(—) a)

Further, the calculation section 78 can be replaced by a calculationsection 86 in FIG. 15 or a calculation section 88 in FIG. 16. Thecalculation section 86 includes maps shown in FIGS. 17 and 18. The mapin FIG. 17 defines relation between demanded acceleration degree Ar_dand acceleration-period target intake pressure Ps_o_1, while the map inFIG. 18 defines relation between exit air temperature Te_b andacceleration-period target intake pressure Ps_o_2.

The calculation section 86 reads the target intake pressures Ps_o_1 andPs_o_2 corresponding to the demanded acceleration degree Ar_d and theexit air temperature Te_b, respectively, and supplies a greater one ofthe two target intake pressures Ps_o_1 and Ps_o_2 to the output section84, for use as a target intake pressure Ps_o_a.

Meanwhile, the calculation section 88 includes maps shown in FIGS. 19and 20. The map in FIG. 19 defines relation between demandedacceleration degree Ar_d and acceleration-period target air temperatureTe_b_1, while the map in FIG. 20 defines relation between exit airtemperature Te_b and acceleration-period target air temperature Te_b_2.

The calculation section 88 reads the target air temperatures Te_b_1 andTe_b_2 corresponding to the demanded acceleration degree Ar_d and theexit air temperature Te_b, respectively, and supplies a greater one ofthe two target air temperatures Te_b_1 and Te_b_2 to the output section80, for use as the target intake pressure Te b_a.

With the calculation section and output section of the types shown inFIGS. 13 to 16, it is possible to ensure the vehicle accelerationperformance and at the same time maintain the comfortable compartmenttemperature Tr, during vehicle acceleration.

Although the control flow chart of FIG. 3 includes steps S307, S308 andS314 for setting the flag, these steps S307, S308 and S314 can beomitted. In that case, the capacity control signal Ia is allowed to bereplaced by a new capacity control signal during vehicle acceleration.

The temperature sensor 30 may be provided to detect the exit-sidesurface temperature of the evaporator 14, in place of detecting the exitair temperature Te_a, i.e., the temperature of air at the exit of theevaporator 14 after passing through the evaporator 14. Further, theaccelerator depression quantity Da can be used in place of the demandedacceleration degree Ar_d.

1. An air-conditioning system for a vehicle, comprising: a refrigerationcircuit including a circulation path along which a refrigerantcirculates, said refrigeration circuit having a variable capacitycompressor, a condenser, an expansion mechanism and an evaporatordisposed in the circulation path in this order; a degree detectiondevice for detecting demanded vehicle-acceleration degree; a temperaturedetection device for detecting temperature of the evaporator ortemperature correlating with the temperature of the evaporator, atvehicle-acceleration start time; a selection device for selectingacceleration-period cooling performance of the refrigeration circuit, onthe basis of the demanded acceleration degree and the temperaturedetected; and an output device for generating a capacity control signalfor determining an amount of the refrigerant discharged from thecompressor, on the basis of the acceleration-period cooling performanceselected, and outputting the capacity control signal to the compressor.2. The system according to claim 1, wherein said selection device havecontrol modes for controlling the acceleration-period coolingperformance of the refrigeration circuit, where selection from thecontrol modes is performed on the basis of a difference betweenpre-acceleration cooling performance of the refrigeration circuit at theacceleration start time and post-acceleration cooling performance of therefrigeration circuit estimated in consideration of vehicleacceleration.
 3. The system according to claim 2, wherein the controlmodes include a HOLD mode to be selected when said difference is withina specified range, for maintaining the acceleration-period coolingperformance at the same level as the pre-acceleration coolingperformance.
 4. The system according to claim 2, wherein the controlmodes include at least one of an UP mode and a DOWN mode to be selectedwhen said difference is out of a specified range; wherein the UP modemaintains the acceleration-period cooling performance at a higher levelcompared with the pre-acceleration cooling performance, and the DOWNmode maintains the acceleration-period cooling performance at a lowerlevel compared with the pre-acceleration cooling performance.
 5. Thesystem according to claim 4, wherein the UP mode is provided to causethe acceleration-period cooling performance to increase with an increasein the temperature detected.
 6. The system according to claim 4, whereinthe DOWN mode is provided to cause the acceleration-period coolingperformance to decrease with an increase in the demanded accelerationdegree.
 7. The system according to claim 1, wherein said selectiondevice calculates an acceleration-period target temperature for theevaporator, on the basis of the demanded acceleration degree and thetemperature detected, and set the acceleration-period coolingperformance on the basis of the acceleration-period target temperature.8. The system according to claim 7, wherein the acceleration-periodtarget temperature is a target temperature for exit air having passedthrough the evaporator.
 9. The system according to claim 1, wherein saidselection device calculates an acceleration-period target pressure forthe compressor, on the basis of the demanded acceleration degree and thetemperature detected, and sets the acceleration-period coolingperformance on the basis of the acceleration-period target pressure. 10.The system according to claim 9, wherein the acceleration-period targetpressure is a target intake pressure at which the compressor should suckin the refrigerant.